A method for driving a stepping motor is described, for example, in German patent publication DD 279 988 A1. Therein, a circuit configuration for the control of a self-clocked stepping motor drive for components, for example printers, is disclosed in which a constant positioning speed must be attained and the start-up and deceleration phase is realized with a maximum motor moment. The driving circuit for the stepping motor, which drives for example the print carriage of a printer, derives from the signals of the motor timing, in real time, driving signals for the winding switch-over of the stepping motor. Through the combination of a stepping motor with a timing system, data about the execution of the driven motor steps is available and as a function of these timing data the selection of the winding can take place such that the particular required motor moment is attained. In order to accelerate the print carriage, as is required in the case of fast printers, in an extremely short time and after a very short print carriage path, to the maximum print carriage speed, a target frequency is set by the driving device to which the stepping motor attempts to accelerate. In operation of the stepping motor drive with impressed load, this target frequency is not achieved, however, and the stepping motor drive rotates without step loss at reduced real step frequency. The detection of the real step frequency at which the stepping motor rotates under load is not addressed in the publication DD 279 988 A1.
However, circumstances are conceivable in which the real step frequency is to be determined when the rotational speed of the stepping motor exceeds or falls below a given speed threshold. This is the case, for example, whenever via a driving device the stepping motor drive is driven at a desired frequency, to reach the target speed. However, due to the condition on load the stepping motor, the stepping motor is more or less strongly decelerated and the occurrence of this load condition is to be determined. This can be the case with document or sheet front-feed devices in which a stepping motor drive is connected to transfer rollers, and the document or sheet is output by only one sheet output unit at a given speed. With the acquisition of the sheet, the load condition occurs.
The invention therefore has the goal of further developing said method such that the load condition can be determined. In addition, the invention has the goal of attaining a device, and circuit configuration, for carrying out such method.